Tribological properties of copper (II) oxide nanoparticle-enriched sandbox bio-lubricant

The demand for bio-lubricant is constantly on the increase due to rapid depletion of world fossil fuel reserves, technological advancement, concern for environmental pollution and its potential to address the energy and environmental problems. This research evaluated the tribological properties of copper (II) oxide nanoparticle-enriched bio-lubricant developed from sandbox (Hura crepitans) seed oil. Copper (II) oxide nanoparticle was added to improve the tribological properties of the bio-lubricant. The experimental parameters were set up according to central composite design of response surface methodology to minimize the numbers of experiments. The bio-lubricants containing varying proportions of copper (II) oxide nanoparticle additive were prepared and their tribological properties were evaluated using ball-on-disc tribometer. The values of parameters used to assess the tribological behaviors were: load (2 N, 5 N, 8 N), speed (150 rpm, 200 rpm, 250 rpm) and nanoparticle concentration (0 wt%, 0.75 wt%, 1.50 wt%). The effects of these parameters on wear rate, friction coefficient and flash temperature parameter were evaluated. The lowest value of coefficient of friction (0.048) was obtained at a speed of 250 rpm and concentration of 0.75 % with load of 5 N. The lowest value of wear rate (0.012) was obtained with load of 5 N, speed of 200 rpm and concentration of 0.75 %. The highest value of flash temperature parameter (0.035) was obtained with load of 5 N, speed of 250 rpm and concentration of 0.75 %. The obtained values complied with the standard specified by American Standards and Testing Materials (ASTM) and compare favourably with conventional lubricant SAE 40 and other bio-lubricants.  The results of the analysis were used for optimizing the parameters to obtain the best lubricant effects. The optimal combination of parameters for minimum coefficient of friction and wear rate as well as maximum flash temperature were found to be: 5.0909 N load, 217.6768 rpm speed and 1.1061 wt% concentration. The overall results revealed that enrichment of sandbox oil with copper (II) oxide nanoparticle improved the tribological behavior of the oil.